The present disclosure relates generally to semiconductor integrated circuit (IC) diagnostics, and more specifically, to methods of non-invasive optical IC diagnostics using light emission from leakage currents in field-effect transistors.
One of the methods of IC diagnostics of semi-conductor devices is physical failure analysis (PFA) using photon emission microscopy (PEM). This method uses visible and near infrared photon emission from transistors, pn junctions, and similar structures to find unexpected device current and make conclusions about the operation of the IC.
PEM can use time integrating detectors (such as CCD cameras, Focal Plane Arrays, etc.) to obtain the data, as well as time-resolved detectors (such as multichannel plate photomultipliers, single photon avalanche diodes, photomultipliers, etc.). The PEM can be performed from both the front-side and backside of an IC.
As the size of transistors decreases, two types of parasitic leakage currents become increasingly important—gate tunneling current (this type of current is also present in some capacitors) and OFF-state drain to source current. Each type of leakage current results in photon emission or, simply, leakage light. In general, the leakage light increases with the increase of leakage current as well as the increase of the voltage difference applied to the device.
One limitation of PEM is that it will identify the high current location, but will not be able to quantify the amount of current. Typically, a separate destructive PFA is required to de-layer and probe the device to determine the current.